<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8" />
    <!-- https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP -->
    <title>保护你的眼</title>
  </head>

  <style>
    body {
      margin: 0;
      padding: 0;
      background: #424c50;
      color: white;
    }
    body {
      width: 100vw;
      height: 100vh;
      display: flex;
      justify-content: center;
      align-items: center;
      flex-direction: column;
      user-select: none;
      letter-spacing: 2px;
    }
  </style>
  <body>
    <h1>每 20 分钟放松一次眼睛，一次 20 秒</h1>
    <h2>多眨眼，每分钟 15 ~ 20 次</h2>
  </body>
</html>
